Franz J. T. Huber

Friedrich-Alexander-University Erlangen-Nürnberg | FAU · Department of Chemical and Bioengineering

In this work, iron-oxide nanoparticle formation in the spray-flame synthesis (SFS) process of the standardized SpraySyn 2.0 burner was investigated in situ using laser-induced incandescence (LII). For the evaluation of these measurements, prior LII-experiments within iron-oxide aerosols (Fe3O4 and α-Fe2O3) with known primary particle size distribut...

For reliable tomographic measurements the underlying 2D images from different viewing angles must be matched in terms of signal detection characteristics. Non-linearity effects introduced by intensified cameras and spatial intensity variations induced from inhomogeneous transmission of the optical setup can lead, if not corrected, to a biased tomog...

In this work, the optical properties of soot particles from a Gülder burner fueled with both ethylene or propane gas were investigated in situ using laser-induced incandescence. The particles in the flame were irradiated with four different laser wavelengths, namely 450 nm, 532 nm, 600 nm and 650 nm. The resulting laser-induced emissions were detec...

In this Letter, we demonstrate, for the first time (to the best of our knowledge), calibration-free imaging of full-frame temperature fields for particle-laden flames using two-line atomic fluorescence (TLAF) of indium. Measurements were carried out in laminar premixed flames with indium precursor aerosol added. The technique is based on the excita...

Semiconductor materials are characterised by a band gap between conduction and valence band, which can either be of direct or indirect nature depending on the crystal momentum. In case of applying the so- called Tauc method to infer the band gap value, both transition types are described by different values for the transition type exponent. In the...

A calibration-free two-line atomic fluorescence (TLAF) setup was designed for optical high-precision temperature measurements in combustion processes, with a focus on a high practical applicability in combustion systems. The setup is split into a mobile fibre-connected sensor head and a separate laser arrangement allowing for versatile application,...

The investigation of droplet and nanoparticle formation in spray flame synthesis requires sophisticated measurement techniques, as often both are present simultaneously. Here, wide-angle light scattering (WALS) was applied to determine droplet and nanoparticle size distributions in spray flames from a standardized liquid-fed burner setup. Solvents...

A one-dimensional premixed ethylene–air flame is investigated regarding the presence of various combustion intermediates and products relevant for the formation of carbonaceous particles for various equivalence ratios and spatial positions using in situ UV–Vis absorption spectroscopy. A laser driven light source in combination with a fast spectrome...

This work presents a new approach for high-speed four-dimensional (3D + t) thermometry using only two high-speed cameras which are equipped with different band pass filters to capture thermal radiation signals at two narrow wavelength bands. With the help of a customized fiber bundle and a beam splitter, a total number of nine projections at each b...

Non-intrusive measurement techniques are required to gain a comprehensive understanding about the processes of soot formation, growth and oxidation. Time-resolved laser-induced incandescence (TiRe-LII), commonly performed 0D or 2D within a flame, has proven to be a very suitable tool for the in situ sizing of soot primary particles. In this work, t...

Emissions from diesel engines can be limited and potentially decreased by modifying the fuel chemical composition through additive insertion. One class of additives that have shown to be particularly efficient in the reduction of the particulates from the combustion of diesel fuels are oxygenated compounds. In the present study we investigate the e...

The morphological parameters of polydisperse aerosolized soot can be found by regressing modeled angularly-resolved elastic light scattering to experimental measurements, but this is an ill-posed problem in the presence of measurement noise or model error. Rayleigh-Debye-Gans Fractal Aggregate (RDG-FA) theory provides a closed-form solution for the...

In spray flame synthesis the processes of spray formation and evaporation of the single droplets greatly affect the morphology and size of particles formed. An in situ measurement of these parameters is thus essential for process control and development. In this work, wide-angle light scattering (WALS) is applied to measure droplet sizes in a spray...

Optical, non-invasive techniques for temperature and mole fraction measurements in flames and other reactive flows are often limited to applications under well-defined laboratory environments. These limitations mainly arise from various prerequisites of the techniques e.g. regarding the optical accessibility of the systems under investigation, its...

For a comprehensive understanding of nanoparticle formation in gas phase processes, such as soot formation, morphological parameters of fractal-like particle aggregates, like the radius of gyration, the fractal dimension and the primary particle size, have to be determined. Often transmission electron microscopy (TEM) is employed for the investigat...

The spatial distribution of soot aggregate size and morphology within a premixed flat flame (McKenna-type burner and ethyne–air mixture at an equivalence ratio of Φ = 2.7) is characterized by two-dimensional multi-angle light scattering (2D-MALS). A profound investigation of such an extended, radially symmetrical sooting flame with 2D-MALS requires...

Soot from combustion processes often takes the form of fractal-like aggregates, assembled of primary particles, both of which obey polydisperse size distributions. In this work, the possibility of determining the primary particle size distribution through time-resolved laser-induced incandescence (TiRe-LII) under the influence of thermal shielding...

In the present work, a novel burner capable of complete pre-vaporization and stationary combustion of diesel fuel in a laminar diffusion flame has been developed to investigate the effect of the chemical composition of diesel fuel on soot formation. For the characterization of soot formation during diesel combustion we performed a comprehensive mor...

Planar droplet sizing (PDS) is a technique relying on the assumption that laser-induced fluorescence (LIF) and Mie scattering optical signals from spherical droplets depend on their volume and surface area, respectively. In this article, we verify the validity of this assumption by experimentally analyzing the light intensity of the LIF and Mie opt...

This paper reports on the quantitative 2D and 3D droplet sizing based on the LIF/Mie ratio in ethanol DISI (Direct Injection Spark Ignition) sprays, where the required calibration is performed using quantitative micro and macro LIF/Mie ratio imaging of individual microdroplets. The droplets are generated from a monodisperse droplet generator in a d...

The paper presents simultaneous high-speed (7.5 kHz) planar laser-induced fluorescence (PLIF) of formaldehyde (CH2O) and the hydroxyl-radical (OH) for visualization of the flame structure and heat release zone in a non-premixed unsteady CH4/O2/N2 flame. For this purpose, a dye laser designed for high-speed operation is pumped by the second-harmonic...

Candidate LII measurement models presented in the literature cannot explain several commonly-observed phenomena in experimental data. A new model is proposed based on electron neutral bremsstrahlung emission and inverse neutral bremsstrahlung absorption during laser-induced incandescence on silver nanoparticles.

The performance of particle‐based products depends on a multiple set of particle properties. To monitor them during particle manufacturing, three novel aerosol measurement techniques were developed: wide‐angle light scattering (WALS), three‐dimensional laser scattering (3D‐LSS), and differential aerodynamic particle sizing (DAPS). They measure part...

In nanoparticle synthesis, a large variety of sizes and morphologies can be observed depending on the process parameters. Besides fractal-like aggregates built from primary particles and non-aggregated spherical particles also mixtures of particle fractions are obtained. For industrial process control, real-time capable algorithms for multi-variate...

Inferring the size distribution of aerosolized fractal aggregates from the angular distribution of elastically scattered light is a mathematically ill-posed problem. This paper presents a procedure for analyzing Wide-Angle Light Scattering (WALS) data using Bayesian inference. The outcome is probability densities for the recovered size distribution...

Cavity-enhanced absorption spectroscopy is promising for many applications requiring a very high concentration sensitivity but often accompanied by low temporal resolution. In this Letter, we demonstrate a broadband cavity-enhanced absorption spectrometer capable of detection rates of up to 50 kHz, based on a spatially coherent supercontinuum (SC)...

A mobile demonstrator for the comprehensive online-characterization of gas-borne nanoparticle aggregates is presented. Two optical measurement techniques are combined, both utilizing a pulsed Nd:YAG laser as light source. Aggregate size and fractal dimension are measured by Wide-Angle Light Scattering (WALS). An ellipsoidal mirror images elasticall...

The applicability of two-line atomic fluorescence (TLAF) for temperature imaging in an indium-based flame spray pyrolysis (FSP) process is demonstrated using a single tunable optical parametric oscillator (OPO) to generate the required excitation wavelengths consecutively. Single-shot images of the detected fluorescence signals demonstrate that the...

In the medical field, the demand for motion-robust 3D data acquisition is steadily growing, e.g. for capturing limbs to construct prostheses. For this purpose, an optical 3D sensor is required which enables a flexible and comfortable 3D capturing of body parts. A " Flying Triangulation " sensor enables such tasks. Two exemplary applications, one in...

In radiation therapy, tracking the patient's non-rigid torso deformation during dose delivery holds potential to improve accuracy and efficiency using model-based tumor motion compensation. Conventional solutions rely on a 1-D respiration sur-rogate and are subject to model uncertainties. Instead, the proposed system acquires sparse 3-D measurement...

Based on the measurement principle " Flying Triangulation " , we present a motion-robust sensor for objects within the meter range, especially for human bodies, sculptures, or rooms. The principle requires neither external tracking nor a still-standing sensor or object. The current measurement progress is displayed in real time. We show recent resu...

Flying Triangulation" is an optical 3D measurement principle, where a single-shot sensor acquires a series of sparse 3D views which then are automatically aligned to each other in real time. Due to its motion robustness and a real-time feedback, complex objects can be measured in a very intuitional way. In this paper we investigate the options and...